The Brothers Grim
"I am very sorry for TBG's loss, as complicated as it is," said Dr. James Cantor, a psychologist, associate professor at the University of Toronto, and editor in chief of Sexual Abuse: A Journal of Research and Treatment. "The quick answer to his question: no. Although it is unusual, having dreams like that does not, by itself, mean a man is gay or otherwise into penises. [OK, technically, it's "penes."] Although there haven't been any formal surveys, gay men usually dream (and fantasize while masturbating) about men in general: muscles and faces, celebrities and crushes, the range of their favorite sex acts, etc. I haven't heard a gay man-friend or client-describe dreams restricted lifelong to just penis-in-mouth."
Dr. Cantor offers a caveat for other readers: "For a long time, many folks believed that such dreams were repressed memories trying to surface. But there was never any good evidence for it. In fact, a great deal of harm has been done by well-meaning 'therapists' who, instead of helping clients to recover lost memories, wound up creating false memories of abuse and destroying whole families." So very clearly and for the record: "Having such dreams, by itself, does not mean a person was abused."
What is odd, however, is the longstanding, repetitive nature of your brother's dreams.
"Although dreams do not tell us anything specific (again, these are not memories-in-waiting or great symbolic themes), they can suggest that there is something on his mind," said Dr. Cantor. "If life is going generally well, and this is just a harmless eccentricity, so be it. If, however, your brother is experiencing more general distress, then that distress-whether fallout from childhood abuse, from the death of your father, or from something else-could be targeted with a bona fide, licensed therapist. Complicated situations like yours almost always involve multiple strong and conflicting emotions. Because you say lots of stuff (other than these dreams) is coming up for you both, an objective outsider/listener can indeed be of great help in sorting it out."
What do you say to a college-age brother who tells you more about his sex life than you want to hear? I love my bro, but I don't need to know how much pussy he's getting. I used to tell him about my "triumphs," but we were in high school then, and I've matured since. He was a late bloomer, he's kind of insecure, and I think he's excited to be doing well socially and sexually. But I don't want to hear about it anymore.